The present invention relates to a mechanism for preventing the breakage of a tilt leg of a terminal device, using a telephone as an application example.
The main points of an installation-angle adjusting mechanism of a device such as a telephone will first be described as a first related art with reference to Japanese Patent Application Publication (JP-A) No. H10-23126.
Referring to FIG. 1, a telephone 31 includes an upper casing 32, a lower casing 33, and a receiver transmitter 34. The upper casing 32 includes a numeric keypad 32a. The lower casing 33 has a first leg 35 rotatably attached to one end of the bottom thereof. The first leg 35 includes a second leg 36 rotatably and slidably attached thereto (the details will be described later). The lower casing 33 has a leg 33a, made of an elastic material such as rubber, attached to the other end of the bottom thereof.
Referring to FIG. 2, a holding section 33b is provided at one end of the bottom of the lower casing 33 for accommodating the first leg 35 and the second leg 36. The holding section 33b has a shaft 33c on side wall 33b1.
FIG. 3 shows a state in which the lower casing 33 is horizontally positioned on a desk 37. The first leg 35 and the second leg 36 are overlaid in the holding section 33b. A leg 35a made of an elastic material such as rubber is attached to one end of the first leg 35. Similarly, a leg 36a is attached to one end of the second leg 36. A leg 36b is attached to the vicinity of the leg 36a in the direction perpendicular to the leg 36a. In this state, the leg 36b is in contact with the desk 37.
FIG. 4 shows a state in which the lower casing 33 is moved onto the desk 37 at a small angle. The first leg 35 rotates approximately at 90 degrees together with the second leg 36 from the holding section 33b in the direction of the arrow around the shaft 33c, and so the leg 35a is brought into contact with the desk 37.
FIG. 5 shows a state in which the lower casing 33 is moved onto the desk 37 at a large angle. The second leg 36 rotates at 180 degrees with respect to the first leg 35 with a shaft-support rotating mechanism (not shown) and then slides in the direction of the arrow with a pin and a guide groove mechanism (not shown), and so the leg 36a is brought into contact with the desk 37.
The main points of an angle adjusting mechanism of a telephone will now be described as a second related art with reference to Japanese Patent Application Publication (JP-A) No. H07-250145.
Referring to FIG. 6 and FIGS. 9 to 11, a telephone 41 includes an upper casing 42, a lower casing 43, and a receiver transmitter 44. The lower casing 43 has a pair of first legs 45 (only one is shown) rotatably attached to one end of the bottom thereof. The first leg 45 has a second leg 46 slidably attached thereto (the details will be described later). The lower casing 43 has a leg 43a attached to the other end of the bottom thereof.
The pair of first legs 45 are joined together with a joint 47. A shaft 48 projects horizontally from the side of each first leg 45. A bearing 49, shown in FIG. 7, is attached to the lower casing 43. The bearing 49 has an inclined surface 49a for the shaft 48 to insert, on the lower inside (upside down in FIG. 7) of the bearing 49. The inclined surface 49a is inclined outward toward the lower end. The bearing 49 has a bearing hole 49b in the center. The shaft 48 of the first leg 45 is pushed into the interior of the bearing 49 through the inclined surface 49a such that it can be inserted in and drawn out from the bearing hole 49b by the elastic deformation of the bearing 49.
The pair of second legs 46 is joined together with a joint 50. Each second leg 46 is supported in the first leg 45 such that it can be inserted therein or protrude therefrom. A guide rib 46a protruding from each second leg 46 is engagement with a guide groove 45a of each first leg 45. The guide rib 46a serves as a guide when the second leg 46 is inserted into or protrudes from the first leg 45. Each first leg 45 has engaging holes 45b and 45c in the upper and lower parts. Each second leg 46 has an engaging protrusion 46b that comes selectively into engagement with the engaging hole 45b or 45c. Referring now to FIG. 8, the engaging protrusion 46b has an inclined surface 46c inclined backward at the lower part. The engaging protrusion 46b can be held in the first leg 45 such that it is inserted therein or protrude therefrom by selectively bringing the engaging protrusion 46b into engagement with the engaging hole 45b or 45c. 
The lower casing 43 and the joint 50 have an engaging protrusion 43b and an engaging hole 50a, respectively, in correspondence with each other. The legs 45 and 46 rotate from the position indicated in FIG. 6 to the position along the bottom of the lower casing 43 of the telephone 41, indicated in FIG. 9, around the bearing hole 49b and the shaft 48, with the second leg 46 inserted in the first leg 45. At that time, the engaging hole 50a is forcedly brought into engagement with the engaging protrusion 43b. 
The outer surface of the first leg 45, or the surface of the first leg 45 in contact with a desk 51 in the normal state shown in FIG. 9, includes a leg 45d mounted thereto. In this state, the telephone 41 is prevented with the legs 43a and 45d from slipping with respect to the desk 51.
The engaging hole 50a is forcedly brought out of engagement with the engaging protrusion 43b in the normal state of FIG. 9 and, as shown in FIG. 10, the legs 45 and 46 are rotated approximately at 90 degrees in the direction of the arrow from the bottom of the lower casing 43. Then an operating surface 42a of the telephone 41 moves to the position at which the inclination angle relative to the desk 51 is increased by a small angle. In this state, the telephone 41 is prevented with the leg 43a of the lower casing 43 and legs 46d of the second legs 46 from slipping with respect to the desk 51.
When each second leg 46 is drawn downward with respect to the first leg 45 in the small-angle inclined state of FIG. 10, the engaging protrusion 46b is brought out of engagement with the engaging hole 45b and brought into engagement with the engaging hole 45c, from the state shown in FIG. 8. Then, as shown in FIG. 11, the operating surface 42a of the telephone 41 moves to the position at which the inclination angle relative to the desk 51 is increased by a large angle. In this state, the telephone 41 is prevented with the legs 43a and 46d from slipping with respect to the desk 51.
The related-art techniques are capable of three-step (more than four steps by design changes) angle adjustment of terminal devices, with the first leg and the second leg as tilt legs. However, measures are not taken at all to prevent breakage of the tilt legs when an excessive load is applied to the terminal devices.